A fire broke out on the roof of Trump Tower early Monday, injuring a firefighter and two civilians, authorities said.

Secret Service agents noticed smoke billowing from the building’s roof and called a fire safety official in the lobby who then located the flames, FDNY Assistant Chief Roger Sakowich said.

The smoky blaze erupted when empty water-storage units caught fire atop the 68-story building at 721 Fifth Ave. just before 7 a.m. The fire was placed under control at 8:13 a.m. No flames were reported inside the building.

One firefighter sustained minor injuries when debris fell on him and was taken to Bellevue Hospital for treatment, according to the FDNY. Two civilians were treated at the scene — also for minor injuries — and declined further medical attention. One was an engineer who went up to the roof with a fire extinguisher and breathed in some of the smoke, Sakowich told reporters Monday.

There were no reported evacuations. Tenants were advised to remain in place.

President Trump, who was in Washington, DC, at the time of the blaze, maintains a penthouse unit in the skyscraper.

His son, Eric Trump, took to Twitter to praise firefighters for their quick response.

“There was a small electrical fire in a cooling tower on the roof of Trump Tower,” he posted. “The New York Fire Department was here within minutes and did an incredible job. The men and women of the #FDNY are true heroes and deserve our most sincere thanks and praise!”

A total of 84 firefighters responded to the blaze in 19-degree weather, Sakowich said.

FDNY Battalion Chief Thomas Dolan told The Post that the cost in damages to the building is “not very much at all.”